There shall be an annual audit by a certified public accountant or other disinterested public accountant of every municipality having according to the most recent federal census as much or more than a population of 2,000 and an audit biennially for municipalities with a population of less than 2,000 according to the most recent federal census. Said audit shall describe in detail each bond issue outstanding and shall disclose the provision made for payment thereof. In the case of assessment bonds it shall show the amount of assessments 12 months or more past due pledged for the payment of each series of bonds and the amount of all other assessments and the estimated deficit, if any, to be paid out of the general revenues of the municipality. One copy of such audit shall be filed with the clerk of the municipality.